In a prior art integrated communication system in which HDLC X.25 computer data packets and fixed-length voice/video packets are transmitted over a common trasmission medium, the fixed-length packets are transformed into the HDLC format and a specified identifier is inserted into the address or control field of the transformed packets so that both types of packets are treated at the receive end as variable-length packets. Because of the adoption of the HDLC format for mixing the different formats, the prior art system employs what is called "zero-insertion and zero-deletion" scheme by forcibly inserting a 0 bit if there is a string of five consecutive 1 bits at the transmit end and removing it at the receive end to allow transmission of a flag pattern "01111110" as a delimiter of the variable-length packet.
However, if disruption occurs in a received data stream causing an error in the inserted 0 bit, the packet containing this error bit is aborted. Otherwise, such a packet propagates along the network as a truncated, short packet or merges with a preceding packet resulting in a long packet. In either case, the packet is detected as an error by a frame check sequence and is eventually discarded. If an error occurs in X.25 HDLC packet, it can be corrected by the packet retransmission scheme, whereas voice/video packets in error are simply discarded. The potential source of this type of error is the bit reversal of the forcibly inserted 0 bit in the voice/video packet. Such irrecoverable errors can occur at 2.1-second intervals for a transmission rate of 1.5 Mbps at a bit error rate of 10.sup.-5. One approach to this problem is to append an error correcting code to fixed-length packets. However, since the beginning and ending points of such packets cannot be guaranteed with a high degree of certainty, the error correcting code approach serves no purpose. Another approach would be to employ a retransmission scheme as in the case of the X.25 packets. However, the real-time transmission requirement of the voice/video packet cannot be met by the retransmission scheme.